Age: As old as the first caveman's primitive cry of "Hey! That looks a bit like a face."

Appearance: A bit like a face. On the moon.

What is it actually? A pattern in the smooth lunar plains – known as maria – on the moon's surface, formed by ancient volcanic eruptions, that appear to us on Earth as patches of relative darkness.

And do they look like a face? A little. Western stargazers have seen a friendly bloke up there since at least the time of the Romans.

Great. What's he done recently? Nothing, really. He has just been staring down at us for about a billion years.

Is that surprising? Quite surprising, when you stop and think about it. Given that both the moon and the Earth are simultaneously spinning on their axes, around each other, and around the sun, you would expect different parts of the lunar surface to be visible at different times. As it is, the man up there never averts his gaze: we always look up at the same side of the moon.

You just broke my mind. Don't worry. We'll fix it with science. A team of physicists from California Institute of Technology and the Hebrew University of Jerusalem have published a paper entitled "Why do we see the man in the moon?" explaining the satellite's remarkable ability to maintain eye contact with the Earth.

And the explanation is? In a nutshell, over time Earth's gravity has pulled the moon into the shape of a rugby ball with the man on one of the pointy ends, and then – as a result of the moon's slowing rotation rate – added a little extra bump to the man's end to keep it steady. Like a rudder or the point of a spinning top.

Or a nose? If you like. And thanks to that nose, after billions of years together, the Earth and the moon have fallen into a synchronous orbit – the moon turns exactly once for each lap of the Earth it performs – ensuring that the same old face is always pointing down at us.